Cassette pumps provide a convenient and relatively low cost device for infusing drugs into the body of a patient. These pumps employ intravenous or IV sets that have pump cassettes made of injection molded plastic, which are discarded after use with a patient. A pump designed to operate with a particular configuration of cassette includes a drive mechanism that actuates the cassette to deliver fluids to a patient. Such pumps are typically controlled by a microprocessor that can be programmed to deliver a predefined volume of medicinal fluid, at a predefined rate, and over a predefined time. Cassette pumps are typically more accurate than peristaltic pumps and are able to deliver drugs at a relatively wide range of rates and volumes.
In a cassette pump disclosed in U.S. Pat. No. 4,865,584, which is assigned to the same assignee as the present invention, the cassette comprises a housing having a front portion that includes openings for valve actuators and a pump plunger, and a rear portion in which passages, valve seats, and a pumping chamber are formed. An elastomeric membrane is sealed between the front and rear portions of the cassette body. The elastomeric membrane seals the passages formed in the rear portion and is displaced by the valve actuators to close valves formed in the housing and by a pump plunger to force fluid through the cassette. Said valves are normally open when outside the pump and are closed by actuators in the pump. The fluid enters the cassette housing through either a primary or a secondary inlet port and is forced through an outlet port under pressure. During an intake stroke, the outlet valve closes, the inlet valve opens, and the pump plunger draws back. The fluid is then drawn through the open inlet valve and into the pumping chamber as the elastomeric membrane covering the pumping chamber pulls back from its prior fully displaced configuration. In a pumping stroke, the inlet valve closes, the outlet valve opens, and the pump plunger forces the elastomeric membrane back into the pumping chamber to force the fluid contained therein through the outlet port.
One problem with the IV set, cassette and pump described in the '584 patent is that free flow of fluid may occur at any time the cassette is not secured in the pump with the outlet valve closed. Free flow is undesirable when the infusion set containing the cassette is fluidly connected to an IV bag containing a drug and the patient because an overdose of the drug can result. If free flow occurs before the cassette is inserted into the pump or connected to the patient, then some of the contents of the IV bag are spilled or lost. This can result in under-delivery of the drug if all of the bag's contents were supposed to be delivered. However, selective free flow of fluid through the cassette would be desirable for manually priming the infusion set with fluid to remove any air before the cassette of the set is inserted into the pump or connected to the patient.
Additionally, in order to avoid causing air embolisms in the patient's blood vessels, conventional procedures require a user of the pump described in the '584 patent to install the cassette in the pump and then perform a special automatic priming procedure using the pumping mechanism to purge the line of air before the set is connected to the patient. It would be advantageous if the user had the flexibility to choose between manual priming, automatic priming or some combination of both to meet their needs, save time or better utilize the pump. A valve or cassette that provides both anti-free flow and priming functions with or without being installed in a pump is needed.
Thus, there is a need in the art for an infusion set with a selectively openable valve that is normally closed and does not have to be closed by a pump mechanism. There is a need for a valve that is always in a closed position until connecting to the pump at which time the valve is automatically opened. Additionally there is a need for an economical cassette with a simplified design compared to the state of the art. Also, improved integrity of a valve that prevents flow through a cassette is desired. Further, elimination of precise control in aligning pieces of the cassette during manufacturing is desired to minimize manufacturing costs.
Thus, a principal object of the present invention is to prevent free-flow when a cassette or IV set is not installed in a pump.
Another object of the present invention is to provide an improved cassette for an intravenous pump, wherein the cassette has a normally closed valve that is automatically opened when the cassette is securely installed in the pump.
Another object of the present invention is to provide a valve or cassette that provides both anti-free flow and priming functions with or without being installed in a pump.
Another object of the present invention is to provide a valve or cassette that gives the user the flexibility to choose between manual priming, automatic priming or some combination of both to meet their needs, save time, or better utilize a pump.
Another object of the present invention is to provide a valve that acts as a pressure actuated check valve.
Another object of the present invention is to provide a valve that acts as a pressure relief valve.
Another object of the present invention is to provide a valve that acts as a pressure actuated check valve in one direction of fluid flow and a pressure relief valve in an opposite direction of fluid flow.
Another object of the present invention is to provide a simplified design for a cassette to minimize costs.
Another object of the present invention is to provide a simplified design for a valve to minimize costs.
These and other objects, features, or advantages will become apparent from the specification and claims.